ModelRefs / Tool Selection — AI Glossary

Tool Selection — AI Glossary

The agent's process of choosing the appropriate tool from its available toolkit to advance a task toward completion.

Overview

Tool selection is a core agent capability: given a task and a list of available tools (with descriptions and schemas), the LLM chooses which tool(s) to invoke and with what arguments. Quality depends on tool description clarity, the model's instruction-following ability, and the number of tools (large toolsets degrade selection accuracy).

Reference details

Topic	agents
Last reviewed	2026-06-24

Example: The boundary between two tools has to be written down

Give an agent `search_docs` (“search the documentation”) and `search_kb` (“search the knowledge base”) and it will pick between them roughly at random, because nothing in either description says which contains what. The model is not failing to reason; it has been handed an ambiguous specification. The fix is in the text: state the boundary explicitly — what each source contains, and when to prefer one — and selection accuracy moves without touching the model. Selection errors are usually specification bugs, and the first thing to try is rewriting the descriptions, not switching to a larger model.

Commonly confused with

Selection is choosing which tool; argument construction is filling it in correctly; execution is your code running it. They fail differently and need different fixes — a well-chosen tool with malformed arguments is a schema problem, not a selection one. Traces should record which tool was chosen and why it was available, or the two are indistinguishable after the fact.

When to use it

Reach for it when:

Any agent with more than two tools, where the choice is a real decision
As the first thing to instrument: log selections and review the wrong ones
Filtering the toolset per request when the catalogue is large, so only plausible tools are offered

Reach for something else when:

Attaching a large catalogue to every request — context cost and confusion both rise
Tools whose descriptions overlap, which makes correct selection impossible by construction
Assuming a bigger model fixes it before the descriptions have been rewritten

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Frequently asked questions

What is Tool Selection?